1. Field of the Invention
The present invention relates to a control device, an RFID tag reading system and an RFID tag reader. More specifically, the present invention relates to a control device and an RFID tag reading system for a reader (for example, a reader/writer) having a reading function for reading so-called RFID tags (radio frequency identification tag, also called as electronic tag), and such an RFID tag reader.
2. Related Art
Among so-called RFID tags, a 950 MHz band passive tag has an available frequency band assigned, which is from 950 MHz to 956 MHz. In this available frequency band, a band actually available in Japan is from 952 MHz to 955 MHz except a guard band. The band can be divided into up to 14 a unit radio channels of 0.2 MHz each, with consideration for spurious regions.
For a 950 MHz band passive tag system, a high-output 950 MHz band passive tag system which can output up to 30 dBm in the band of 952 MHz to 955 MHz, and a low-output 950 MHz band passive tag system which can output up to 10 dBm are disclosed. The high-output 950 MHz band passive tag system is a reader/writer requiring licensing of radio broadcasting, installed and operated in particular premises, which is mainly used for business purposes. On the contrary, the low-output 950 MHz band passive tag system is a reader/writer not requiring licensing, which is for consumer use such as reading a single or small number of passive tags in a stock room of retail shops and supermarkets or in a production line of factories (e.g., Draft Report of The Low-Power Radio Systems Committee, Information and Communications Technology Sub-Council, Information and Communications Council, online, searched on Nov. 16, 2006, see URL: http://www.soumu.go.jp/s-news/2005/pdf/050808—5—1.pdf, hereinafter referred to as Non-patent Document 1).
An RFID tag reader of the high-output 950 MHz band passive tag system and an RFID tag reader of the low-output 950 MHz band passive tag system can be used in the same premises. For example, an RFID tag reader of the high-output 950 MHz band passive tag system may be located at the entrance of a room. Employees can be equipped with an ID card with an RFID tag included for authentication, and the tag read by the RFID tag reader of the high-output 950 MHz band passive tag system for security management. In addition, an RFID tag reader of the low-output 950 MHz band passive tag system can be installed in the vicinity of each PC in the same room, to check the user's usage permission for the PC by reading the RFID tag for authentication. In many other cases, an RFID tag reader of the high-output 950 MHz band passive tag system and an RFID tag reader of the low-output 950 MHz band passive tag system can be installed in the same premises.
In both the high-output 950 MHz band passive tag system and the low-output 950 MHz band passive tag system, the RFID tag reader can be unable to read the RFID tag properly in the presence of another RFID tag reader in the vicinity thereof, due to: interference between two RFID readers, or between an RFID reader and an RFID tag not designated therefor; and communication congestion and collision due to interference between emitted radiowaves or channel interference in the same frequency band.
It is an object of the present invention to provide a technology for avoiding communication congestion and collision by effectively assigning a unit radio channel for transmission and reception to RFID tag readers using the same unit radio channel group.